Highly anisotropic molecular thin films have been successfully prepared by depositing bisazo dyes under vacuum through evaporation on an oriented poly(tetrafluoroethylene) (PTFE) surface aligned by rubbing or a friction-transfer technique. Polarized absorption spectra (UV−visible and IR), electron diffraction, optical microscopy, and Raman scattering were employed to investigate the molecular orientation in the films. The results indicate that the dye molecules are oriented with their long axes parallel to the PTFE chains and that their phenyl rings are fairly parallel to the substrate surface. Slight modifications of the dye molecules lead to significant changes in the degree of the orientation. In particular, the films from a bisazo dye containing a pyrrolidinyl group exhibit a remarkable orientation, showing dichroic ratios up to 130 on the polarized UV−visible spectra.

We have designed, synthesized and evaluated dibenzothiophenylacetylene homologues as new heterocyclic molecules which were expected to have high Da values and short wavelength UV absorption spectra. The dibenzothiophenyl acetylene homologues exhibited wide nematic phase ranges and had very high extrapolated Dn of over 0.6 and directly measured values of 0.5. The compounds with two dibenzothiophenyl rings were colourless, so that we have succeeded in obtaining colourless super-high Dn liquid crystals. We have also analysed the contribution of the transition band to the refractive indices and the birefringence. From the analysis, the main origins of Dn for compounds 1 and 2 are lower MOs than the HOMO and this results in the compatibility of large Dn and lack of colour. The dibenzothiophenylacetylene compounds behaved according to our design expectations.

Optical properties in conjugated polymers such as poly(p-phenylenevinylene) and poly(9,9-dialkyl-fluorene) have been studied using time-dependent density functional theory. In the calculations of the optical properties, real-space and real-time techniques are employed. We follow the linear responses of the systems under externally applied perturbations in the real time. To estimate the polymer spectra, we have calculated the responses of oligomers of different lengths and obtained the extrapolated values. The estimated polymer spectra agree with the experiments reasonably well.

On the basis of the density-functional theory with lhe use of the hyperneltedchain approximation, a set of integral equations for the ion-ion and electronion radial distribution functions (RDFs) have teen derived lor a liquid metal as a nucleus-electron mixture; its liquid and elecmnic swctures can be determined f" the atomic number 2,. This formulation is applied 10 liquid metallic sodium at temperature 100 V, these integral equations are solved in a self-consistent manner to obtain the ion-ion and eleclron-ion RDFS, the electron-density distribution of a pseudoatom p(r), and the effective interatomic potential & ( r ) at the Same time. m e ion-ion S~NC~UK factor of Na at 100 "$ thus calculated, show an unllent agreement with the experiment as well ar the ion-ion RDF, the effective interammic potential velf ( r ) giving this ion-ion RDF indicates a quite similar behaviour to that utracted from the measured swcture factor by Reatto a d, espeeialfy near the repulsiveare region. However, the elenmn-ion RDF and lhe pseudoatom-electron density p(r), obtained recenlly f " lhe difference beween structure factors ftom x-ray and neutron experiments, show large deviations from lhe calculated ones; this means lhal lo utracl lhese quantities the experiment should be performed in a more precise manner. For comparison, an effective interatomic potential B mnstrueted by the use of the Ashcroft pseudopotential with a mre radius 0.905 A, which )ields almost lhe Same electron-ion RDF and the Same screening charge p(r) ucept near the mre region in addition to the ionion RDF as obtained by the full selfmnsistenl method, the Ashcroft pseudopotential is shown IQ be appropriate in veating liquid Na in mntrast with liquid ti. where it is totally invalid.

Highly anisotropic thin molecular films have been successfully prepared by depositing a bisazomethine dye under vacuum through evaporation on friction-transferred (FT) poly(tetrafluoroethylene) (PTFE) layers. The layers induce the high orientational degrees showing high dichroic ratios over 20 in their polarized UV–visible absorption spectra. Moreover, by modifying FT layers with the further PTFE evaporated and rubbing, the ratios are improved to remarkable values up to 44.